What if a bacterial infection could prevent you from getting Dengue Fever? Malaria too?
Before you run off to eat a handful of spoiled sushi or roll about in a cow pasture allow me to clarify. It isn’t you that needs to become infected, it is the mosquitoes that spread these diseases.
Dengue Fever and malaria are common diseases of the tropics. Both are spread through by the bite of infected mosquitos, which in turn acquire the pathogens by feeding on an infected host. At the turn of the twentieth century both Ronald Ross and Alphonse Laveran were separately recognized with the Nobel Prize for their contributions to our understanding of how malaria is transmitted from person to person.
Malaria was once common in the southeastern U.S. but today it has been effectively eliminated. This was accomplished not by curing those who carried the parasite, but by reducing the rate of infection. Fewer infected people meant fewer infected mosquitoes leading to fewer infected people… well, you get the idea. And to do this all that was required was to keep mosquitoes from biting people!
As anyone who ventures out on a summer night knows this is easier said than done, especially in a part of the country where short winters provide the only respite from the onslaught of these real life vampires.
A combination of events brought this about. The migration of people from rural areas to cities, the aggressive use of pesticides and the draining of swamps all contributed. But the single most effective measure was one that was decidedly low-tech. Screened doors and windows. The species of mosquito most commonly associated with malaria tends to feed in the evening. With more and more people safely behind the protection of fine mesh the cycle of transmission was effectively broken and malaria in the U.S. became a memory.
But what about the rest of the world that cannot afford well screened homes? And what about the more aggressive pathogens such as the virus that causes Dengue? The solution may lie with a humble bacterium.
Wolbachia is a naturally occurring organism that infects somewhere between 60-70% of all insect species and can change the nature of its host. Not only that but unlike most other bacteria Wolbachia can be passed from mother to offspring via eggs, effectively creating an entire population of infected bugs.
In a landmark 2008 paper Scott O’Neil of the University of Queensland demonstrated that infection with Wolbachia could actually protect some insects from viral infections. What had been thought to be a benign symbiont was actually a beneficial partner for the insect.
Then O’Neil got an idea. What if he could infect mosquitoes with a strain of Wolbachia that would “protect” them from the Dengue virus? People might still suffer annoying bites but they would be spared the painful agony that has earned Dengue the nickname “breakbone fever.”
In 2011 O’Neill and co-workers reported that they had developed just such a strain of mosquitoes that are immune to the Dengue virus. Later that year, working with colleagues at James Cook University they intentionally released Wolbachia infected mosquitoes in the area around the resort city of Cairns in northern Queensland.
Preliminary results suggest that the disease resistant mosquitoes are competing well with the natural population and are maintaining their immunity to transmitting Dengue. Within a few years the citizens of Cairns may no longer fear contracting Dengue, even if they will still suffer annoying bites from the mozzies.
Now comes word that American and Chinese researchers have teamed up to develop mosquitos infected with a different strain of Wolbachia. A strain that can block the transmission of the big “M” itself. Malaria.
In laboratory tests the Wolbachia infection is passed down from female mosquitoes to their young, and those that have the bacteria are resistant to contracting the most dangerous strain of human malaria, Plasmodium falciparum. Field trials are planned. If the success of the Cairns project is any indication in coming years the threat of malaria may become as distant a memory for the three and a half billion people who are currently at risk as it is for those who live in the comfort and safety of well screened homes.
One day we may be similarly protected from West Nile virus, Yellow fever, equine encephalitis, and most other mosquito-borne diseases. This would make those annoying welts a little easier to tolerate.